1. Field of the Invention
The present invention relates to a power converter to be suitably utilized for an inverter and a signal level converter to be suitably utilized for the power converter and more particularly to an improvement for increasing a breakdown voltage of the device without requiring a complicated manufacturing process while maintaining a stable operation.
2. Description of the Background Art
In a signal level converting circuit to function as an interface between a power switching element and an MPU (microcomputer) for driving and controlling the power switching element, conventionally, a photocoupler has been used for electrical insulation. In recent years, however, an HVIC (High Voltage Integrated Circuit) has been used because of advantages such as a small size, a low cost and a long lifetime.
FIG. 16 is a block diagram showing a conventional inverter using the HVIC. An inverter 150 comprises three power converters 151 to 153 having the same structure. The three power converters 151 to 153 share each of three-phase outputs U, V and W. Each of the power converters 151 to 153 is provided between a high potential power line PP and a low potential power line (grounding conductor) NN and receives the supply of a d.c. source voltage from an external power source 165. Moreover, a control signal is input from an external microcomputer 160 to each of the power converters 151 to 153.
The power converter 151 includes power switching elements 172 and 173, free wheel diodes 174 and 175, a capacitor 170 and an HVIC (High Voltage Integrated Circuit) 154. In an example of FIG. 16, the power switching elements 172 and 173 are IGBTs (Insulated Gate Bipolar Transistors). A load is connected through a wiring OUT (U) to a connecting portion of the power switching elements 172 and 173 connected to each other in series.
The HVIC 154 includes a buffer 166, driving circuits 169 and 171, a switching element 167 and a resistive element 168. In the example of FIG. 16, the switching element 167 is an N-channel type high voltage MOSFET. A source voltage is supplied from an external d.c. power source 161 to the buffer 166 and the driving circuit 171. A voltage held by the capacitor 170 is supplied as a source voltage to a driving circuit 169 changing a source potential together with the wiring OUT (U). When the power switching element 173 is turned ON or OFF, the d.c. power source 161 repetitively charges the capacitor 170 through a resistive element 163 and a diode 164.
A level of a signal to be transmitted is varied between the buffer 166 and the driving circuit 169. A series circuit of the switching element 167 and the resistive element 168 which is provided between the buffer 166 and the driving circuit 169 functions as a level shift circuit for converting a level of a signal between the buffer 166 and the driving circuit 169. Accordingly, a breakdown voltage which is equal to or higher than that of the power switching element 172 is required for the switching element 167.
The HVIC has problems, for example, if a breakdown voltage becomes higher, a manufacturing process is more complicated, a manufacturing apparatus is to be introduced newly, a malfunction of the HVIC itself cannot be prevented easily, and the like. In the HVIC, a technique for isolating a low voltage portion from a high voltage portion is a key technology. A junction isolation technique and a dielectric isolation technique have been known as the isolation technique. In the junction isolation technique, an isolation island is formed of an isolating p+ layer by using a method standardly utilized in a normal IC or LSI, and an element or a circuit as an element group is formed on the inside thereof. In the dielectric isolation technique, each of single crystal silicon islands forming each element or circuit is surrounded by a dielectric (for example, a polycrystalline silicon). Consequently, the islands are electrically insulated from each other.
The junction isolation technique has such an advantage as to be carried out by a conventional IC manufacturing apparatus. In some cases, however, a noise current flows to a floating capacitance in an isolation region through dv/dt (a rate of change in a voltage) during a switching operation so that an operation of the circuit is affected. There is a problem in that the phenomenon presents itself more remarkably when a breakdown voltage is increased. The dielectric isolation technique includes a special process such as the bonding of a silicon substrate. Therefore, there is a problem in that a manufacturing process is complicated and a cost per unit chip area is increased. In addition, as a breakdown voltage is more increased, the manufacturing process becomes more complicated so that the cost is more increased.
Up to the present, an HVIC having a breakdown voltage of 600 V has been put on the market. However, if the breakdown voltage is to be more increased, the above-mentioned problems actually arise. Therefore, an increase in the breakdown voltage of the HVIC has not been implemented.
In order to solve the above-mentioned problems in the conventional art, it is an object of the present invention to provide a power converter and a signal level converter which can increase a breakdown voltage without requiring a complicated manufacturing process while maintaining a stable operation.
A first aspect of the present invention is directed to a power converter comprising a first switching element having first and second main electrodes, a second switching element having third and fourth main electrodes, the fourth main electrode being connected to the first main electrode, a first driving circuit to drive the first switching element based on a first control signal input from an outside, a second, driving circuit to drive the second switching element based on a second control signal input from an outside, and n level shift circuits connected in cascade in n stages, the n being an integer of 2 or more, and configured to level shift the first control signal in the n stages and to transmit the level shifted signal to the first driving circuit.
A second aspect of the present invention is directed to the power converter according to the first aspect of the present invention, further comprising a sense circuit to detect an operation state of the first switching element and to output a detection signal representing the operation state, and n other level shift circuits connected in cascade in n stages and configured to level shift the detection signal in the n stages and to transmit the level shifted signal to an outside.
A third aspect of the present invention is directed to the power converter according to the second aspect of the present invention, further comprising a one-shot pulse circuit connected to an input of each of the n other level shift circuits, and a latch circuit connected to an output of each of the n other level shift circuits.
A fourth aspect of the present invention is directed to the power converter according to any of the first to third aspects of the present invention, further comprising a one-shot pulse circuit connected to an input of each of the n level shift circuits, and a latch circuit connected to an output of each of the n level shift circuits.
A fifth aspect of the present invention is directed to the power converter according to any of the first to fourth aspects of the present invention, wherein each of the n level shift circuits includes a resistive element and a switching element which are connected to each other in series.
A sixth aspect of the present invention is directed to the power converter according to the second aspect of the present invention, wherein each of the n other level shift circuits includes a resistive element and a switching element which are connected to each other in series.
A seventh aspect of the present invention is directed to the power converter according to any of the first to sixth aspects of the present invention, further comprising a voltage dividing circuit having one end connected to the third main electrode and the other end connected to the first main electrode and configured to divide an electric potential of the one end and an electric potential of the other end, thereby outputting first to (nxe2x88x921)th intermediate potentials, first to nth diodes connected to each other in series in the same direction, and first to nth capacitors, wherein one end of the first to nth capacitors are respectively connected to one electrode of the first to nth diodes, and the other end of the first to nth capacitors are connected to an output of the first to (nxe2x88x921)th intermediate potentials and the first main electrode, respectively.
An eighth aspect of the present invention is directed to the power converter according to the seventh aspect of the present invention, wherein the voltage dividing circuit includes first to nth resistive elements which are connected to each other in series, and the first to (nxe2x88x921)th intermediate potentials are output from (nxe2x88x921) connecting portions from the first to nth resistive elements, respectively.
A ninth aspect of the present invention is directed to the power converter according to the eighth aspect of the present invention, further comprising (nxe2x88x921) diodes connected to the second to nth resistive elements in parallel, respectively.
A tenth aspect of the present invention is directed to the power converter according to any of the seventh to ninth aspects of the present invention, further comprising n diodes connected to each other in series, a pair of power terminals of the first driving circuit being connected to the one end of the nth capacitor and the other end thereof, respectively, and one of a pair of power terminals of the second driving circuit being connected to the third main electrode and the other of the pair of the, power terminals being connected to one end of a series circuit of the n diodes.
An eleventh aspect of the present invention is directed to the power converter according to any of the seventh to tenth aspects of the present invention, further comprising n resistive elements connected to the first to nth diodes in parallel, respectively.
A twelfth aspect of the present invention is directed to the power converter according to any of the seventh to eleventh aspects of the present invention, further comprising another resistive element connected to the first diode in series.
A thirteenth aspect of the present invention is directed to the power converter according to any of the first to twelfth aspects of the present invention, further comprising first and second free wheel diodes connected to the first and second switching elements in antiparallel, respectively.
A fourteenth aspect of the present invention is directed to a signal level converter comprising a voltage dividing circuit having one end connected to a first potential line to transmit a first potential and the other end connected to a second potential line to transmit a second potential and configured to divide the first potential and the second potential, thereby outputting first to (nxe2x88x921)th intermediate potentials, first to nth diodes connected to each other in series in the same direction, first to nth capacitors, which have one end respectively connected to one electrode of the first to nth diodes and the other end respectively connected to an output of the first to (nxe2x88x921)th intermediate potentials and the second potential line, and n level shift circuits connected in cascade in n stages, the n being an integer of 2 or more, and configured to level shift one of a signal based on the first potential and a signal based on the second potential in n stages and to thereby convert the same into the other signal.
A fifteenth aspect of the present invention is directed to the signal level converter according to the fourteenth aspect of the present invention, further comprising a one-shot pulse circuit connected to an input of each of the n level shift circuits, and a latch circuit connected to an output of each of the n level shift circuits.
A sixteenth aspect of the present invention is directed to the signal level converter according to any of the fourteenth to fifteenth aspects of the present invention, wherein each of the n level shift circuits includes a resistive element and a switching element which are connected to each other in series.
A seventeenth aspect of the present invention is directed to the signal level converter according to any of the fourteenth to sixteenth aspects of the present invention, wherein the voltage dividing circuit includes first to nth resistive elements which are connected to each other in series, and the first to (nxe2x88x921)th intermediate potentials are output from (nxe2x88x921) connecting portions from the first to nth resistive elements, respectively.
An eighteenth aspect of the present invention is directed to the signal level converter according to the seventeenth aspect of the present invention, further comprising (nxe2x88x921) diodes connected to the second to nth resistive elements in parallel, respectively.
A nineteenth aspect of the present invention is directed to the signal level converter according to any of the fourteenth to eighteenth aspects of the present invention, further comprising n resistive elements connected to the first to nth diodes in parallel, respectively.
A twentieth aspect of the present invention is directed to the signal level converter according to any of the fourteenth to nineteenth aspects of the present invention, further comprising another resistive element connected to the first diode in series.
According to the first aspect of the present invention, the control signal is level shifted in a plurality of stages. Therefore, it is possible to raise the breakdown voltage of the device without increasing a breakdown voltage required for each of the level shift circuits. Since a high breakdown voltage is not required for each of the level shift circuits, it is possible to enhance the breakdown voltage of the device without requiring a complicated manufacturing process while maintaining a stable operation.
According to the second aspect of the present invention, the detection signal is level shifted in a plurality of stages. Therefore, it is possible to increase the breakdown voltage of the device shift circuits and to transmit an operation state of the switching element (for example, a current and a temperature) to an external device without raising the breakdown voltage required for each of the level.
According to the third aspect of the present invention, the detection signal is converted into a one-shot pulse form and is then level shifted, and is restored to have an original waveform by the latch circuit. Therefore, it is possible to achieve the level shift of the detection signal while reducing a power loss in the level shift circuit.
According to the fourth aspect of the present invention, the control signal is converted into a one-shot pulse form and is then level shifted, and is restored to have an original waveform by the latch circuit. Therefore, it is possible to achieve the level shift of the control signal while reducing a power loss in the level shift circuit.
According to the fifth aspect of the present invention, each level shift circuit is simply constituted by using the resistive element and the switching element which are connected to each other in series.
According to the sixth aspect of the present invention, each level shift circuit is simply constituted by using the resistive element and the switching element which are connected to each other in series.
According to the seventh aspect of the present invention, the source potentials of the first driving circuit and the n level shift circuits are generated by a simple structure using the voltage dividing circuit, the first to nth diodes, and the first to nth capacitors.
According to the eighth aspect of the present invention, the voltage dividing circuit is simply constituted by using the first to nth resistive elements which are connected to each other in series.
According to the ninth aspect of the present invention, the (nxe2x88x921) diodes are connected to the second to nth resistive elements in parallel with each other. Therefore, a high speed switching operation can be implemented more stably.
According to the tenth aspect of the present invention, the n diodes connected to each other in series are connected to one of the power terminals of the second driving circuit. Therefore, it is possible to eliminate a difference between the source voltage of the first driving circuit and the source voltage of the second driving circuit which arises from forward voltages of the first to nth diodes.
According to the eleventh aspect of the present invention, the n resistive elements are connected to the first to nth diodes in parallel. Therefore, the high speed switching operation can be implemented more stably.
According to the twelfth aspect of the present invention, the resistive element is connected to the first diode in series. Therefore, it is possible to reduce a rush current flowing to the first to nth diodes and the first to nth capacitors.
According to the thirteenth aspect of the present invention, the free wheel diode is connected to each of the first and second switching elements. Therefore, it is possible to utilize the device for an inverter or the like without connecting the free wheel diode to an outside.
According to the fourteenth aspect of the present invention, the signal is level shifted in a plurality of stages between the signal based on the first potential and the signal based on the second potential. Therefore, it is possible to increase a level shift range without raising a breakdown voltage required for each of the level shift circuits. In addition, the source potentials of the n level shift circuits are generated by a simple structure using the voltage dividing circuit, the first to nth diodes, and the first to nth capacitors.
According to the fifteenth aspect of the present invention, the signal is converted into a one-shot pulse form and is then level shifted, and is restored to have an original waveform by the latch circuit. Therefore, it is possible to achieve the level shift of the signal while reducing a power loss in the level shift circuit.
According to the sixteenth aspect of the present invention, each level shift circuit is simply constituted by using the resistive element and the switching element which are connected to each other in series.
According to the seventeenth aspect of the present invention, the voltage dividing circuit is simply constituted by using the first to nth resistive elements which are connected to each other in series.
According to the eighteenth aspect of the present invention, the (nxe2x88x921) diodes are connected to the second to nth resistive elements in parallel. Therefore, also in such a utilization configuration that a difference between the first potential and the second potential is changed at a high speed, the stable operation of the device can be implemented.
According to the nineteenth aspect of the present invention, the n resistive elements are connected to the first to nth diodes in parallel. Therefore, also in such a utilization configuration that a difference between the first potential and the second potential is changed at a high speed, the stable operation of the device can be implemented.
According to the twentieth aspect of the present invention, the resistive element is connected to the first diode in series. Therefore, it is possible to reduce a rush current flowing to the first to nth diodes and the first to nth capacitors.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.